The present disclosure relates to construction and packaging of a power supply. More specifically, the present disclosure relates to construction and packaging of a three-phase power supply using modular electronic modules.
Power supplies configured to control a flow of energy between a first alternating current (AC) system and a second AC system are used in a variety of commercial and industrial applications. For example, a power supply is typically used in AC motor control and operation systems. Various power supplies convert energy from a first frequency and voltage to a second frequency and voltage. One way to implement such a power supply is a drive including one or more power cells, each power cell including multiple solid state converters with an intermediate direct current (DC) link. One exemplary system incorporating such power cells is discussed in U.S. Pat. No. 5,625,545 to Hammond (the '545 patent), the disclosure of which is hereby incorporated by reference in its entirety.
Typically, a power supply such as that discussed in the '545 patent packaged in a single enclosure for easier transportation and set-up. FIG. 1 illustrates a power supply 100 packaged in a multi-cabinet enclosure 102. The enclosure 102 arranges the various components of the power supply 100 in a linear fashion. At one end of the enclosure 102, an input connector 104 is provided for operably connected the power supply 100 to a multi-phase input. In this example, input connector 104 is a configured for a three-phase power input. The input connector 104 is operably connected to a transformer 106 contained within a transformer cabinet in enclosure 102. The transformer 106 typically includes a single primary winding and multiple secondary windings. As discussed in the '545 patent, one example of such a transformer includes a single primary winding and nine secondary windings.
A plurality of power cells 108 are included within a power cell cabinet in the enclosure 102. Each of the power cells 108 is connected to a single secondary winding of the transformer 106. Each of the power cells 108 includes a chassis, a heat sink, a plurality of capacitors, a plurality of bus bars, various insulated gate bipolar transistors (IGBTs) and a plurality of diodes arranged and configured such that the power cell produces a single-phase output in response to a multi-phase input.
Each power cell may include an H-bridge assembly such as those shown in FIGS. 1b and 1c. As shown in FIG. 1b, a half-bridge design 120 may include, for example, a pair of solid state switches 122, 123 connected with each other in series, but in parallel with a capacitor 121. Alternatively, as shown in FIG. 1b, a Perfect Harmony H-bridge design 130 may include two pairs of solid state switches 124a, 124b and 125a, 125b may be connected in parallel with a capacitor 121.
The various power cells 108 may be arranged into columns or rows, each column or row related to a single rank or phase of the power cells. For example, four power cells 108 are arranged into row 110a, four power cells are arranged into row 110b, and four power cells are arranged into row 110c. Each of the four power cells 108 in any given row is operably connected and configured to contribute to a single output. For example, each of the power cells 108 may be configured to produce 750 volts. Thus, power cell row 110a produces a maximum of 3000 volts line-to-neutral at a first phase, power cell row 110b produces a maximum of 3000 volts line-to-neutral at a second phase, and power cell row 110c produces a maximum of 3000 volts line-to-neutral at a third phase. As used herein, 3000 volts neutral may correspond to 5196 volts line-to-line. The three-phase power output by the power cell rows 110a, 110b and 110c is passed to a three-phase output connector (not shown in FIG. 1) where a load such as a motor may be operably attached to the power supply 100.
The power supply 100 also includes various control circuitry 112. The control circuitry 112 is configured to monitor the input at the primary winding of transformer 106, monitor the output of the secondary windings, monitor the operation of each of the power cells 108, and perform other various functions related to the operation of the power supply such as control ventilation through the enclosure 102. The control circuitry 112 is typically operably connected to an exterior control panel or a remote computing device. A user may monitor the operation of the power supply at the control panel or remote computing device, and alter various aspects of the operation of the power supply.
FIG. 1d illustrates an arrangement using an M2C half-bridge assembly (such as assembly 120 as shown in FIG. 1b). Which two or more modular multilevel converter systems 141, 142 are connected in parallel to a DC power source (identified by the P-N inputs) to form an inverter that delivers power to two or more loads 143, 144. Each system includes three inverter legs 145, 146, 147 made up of a set of series-connected inverter submodules 148a, . . . 148n. Although FIG. 11 shows eight submodules in each leg, any number of submodules are possible.
FIG. 1d also includes an expanded view of an exemplary submodule 150. The submodule includes two power semiconductors T1, T2 that are connected in series and which can be switched on and off. The semiconductors T1, T2, also referred to as solid state switches, may be insulated gate bipolar transistors (IGBTs), gate turn-off thyristors (GTOs) integrated gate-commutated thyristors (IGCTs) or the like. Each power semiconductor has a corresponding diode D1, D2 connected in parallel with it. An energy storage device such as a capacitor is connected in parallel with the semiconductors and diodes. Additional details about such a submodule are disclosed in U.S. Pat. No. 7,269,037 to Marquardt, and U.S. Pat. No. 7,960,871 to Dommaschk et al., the relevant disclosures of which is incorporated herein by reference.
Each inverter leg has a single-phase AC output 151, 152, 153 that supplies one phase of three-phase power for the load 143. The AC output is positioned at a midpoint such that an equal number of submodules are on either side of the AC output's electrical connection to the leg.
FIG. 1e illustrates a circuit diagram of a single phase bridge 160 of a five level inverter which combines two NPC (neutral point clamped) three level phase legs 161 with a common DC bus (with a positive rail 162, a negative rail 163, and a midpoint 164) to provide an NPC H-bridge. The NPC three level phase legs include electrical switches 165 which are shown as IGBTs (Insulated Gate Bipolar Transistors). Other useful switches include UFOs (Gate Turn Off Thyristors) and IGCTs (Integrated Gate Commutated Thyristors). The switches are paired with anti-parallel freewheeling diodes 166 to accommodate the inductive motor load currents. A controller 167 is used for controlling each of the switches. The controller may comprise, for example, a computer, a microcomputer, a microprocessor, or, in a preferred embodiment, a digital signal processor.
A capacitor 168 bank 169 midpoint (at DC midpoint 164) and the clamping diodes connected between capacitor bank midpoint and switches S1/S2 and S3/S4 respectively keep the maximum DC working voltage across any switch from exceeding one half of the DC bus voltage (Vdc/2), provided the DC filter capacitor midpoint voltage is maintained at Vdc/2, Regulators are built into the modulator to keep the midpoint voltage at Vdc/2 to guard against long term unequal discharge of the two capacitor bank halves. The resistor network 170 across the DC bus capacitor bank serves as a fixed safely bleed resistor and a balance network for initial capacitor charging. An example of such a bridge is further taught in U.S. Pat. No. 6,058,031 issued May 2, 2000 to Lyons et al. and entitled “Five Level High Power Motor Drive Converter and Control System,” the content of which is hereby incorporated by reference in its entirety.
Power supplies such as power supply 100 are commonly used as motor drives in remote areas or areas where space is limited. The multi-cabinet design of the enclosure 102 provides for easier transportation as each cabinet is transported separately and operably connected and configured on site. However, this arrangement requires a space around the power supply for maneuvering the individual cabinets into place, and, once the cabinets are assembled, the completed enclosure occupies a large footprint. It should be noted that while power cells configured to produce 750 volts are shown in the example above, other power cells may be used. For example, power cells configured to produce from about 480 volts to about 1375 volts may be used.